Method of flame drilling with abrasives



Aug. 26, 1969 BROWNlNG ET AL 3,463,249

' METHOD OF FLAME DRILLING WITH ABRASIVES Filed April 29. 1968 2 Sheets-Sheet l Aug. 26, 1969 BROWNING ET AL 3,463,249

METHOD OF F-L-AML DRILLING WITH ABRASIVES Filed April 29, 1968 2 Sheets-Sheet 2 ABRAS/VE/A/ 044 //v r A? //v United States Patent US. Cl. 175--14 6 Claims ABSTRACT OF THE DISCLOSURE This invention is in the field of cutting rock and other mineral materials. A high velocity flame jet is produced by burning a hydrocarbon fuel with air in a combustion chamber under high pressure. The resulting jet stream composed of the products of combustion and nitrogen is directed against the rock or mineral mass. Abrasive particles may be added as to aid in cutting where required.

Our invention relates to the drilling of holes and the cutting of channels in rock and soils. In particular the principles involved provide for increased working speeds for a given hole or channel as compared to conventional flame jet drilling.

Flame jet drilling and channelling is accomplished using two basically different techniques. Where the rock or soil is susceptible to working by heat action of the flame, said flame alone is capable of producing the drilled hole. Many of the harder rocks are flame drilled in this manner. They include granite, taconite, dolomite, and quartzite among others.

Many common rocks are not capable of being drilled using the flame alone. In these cases a stream of abrasive particles is accelerated to high velocity 'by the flame jet and impacted against the rock surface. A mechanical cutting action results. For further details of this process see [1.8. Patent No. 2,990,653, issued July 4, 1961, to James A. Browning.

In a continuing research program directed towards improving the flame drilling process, we have encountered a basic disadvantage in the present conventional method. We are aware that internal burners have been proposed using oxygen and combustion chamber pressures of up to 175 p.si.g. Such burners are expensive to operate (because of the oxygen). In order to produce holes larger than the diameter of the burner, a major portion of the products of combustion is directed through one or more nozzles directed at an angle away from the axis of the burner.

On the other hand, when air is used as the oxidant and delivered at conventional pressures of 100 p.s.i. the hole produced by an axially directed jet is much larger than the burner diameter. We have found that holes produced using 100 p.s.i. air are frequently much too large to be of practical use. For example, a 600 s.c.f.m. unit will produce a -inch diameter hole in granite. It is very desirable to be able to reduce this diameter to 6 inches and even smaller. Using pure oxygen as the oxidant, this problem does not exist as the axial jet does then produce a small diameter hole. With oxygen, as stated above, the jets must be angled outwardly from the axis.

In our research program we have found that when using air as the oxidant, the hole diameter is closely and inversely related to the pressure maintained in the combustion chamber of the burner. That is, chamber pressures above 150 p.s.i.g. lead to increased drilling speeds with smaller cross-sectional hole area, approaching as a limit, of course, the size of the burner itself. This effect depends in part on the fact that the nitrogen component in 3,463,249 Patented Aug. 26, 1969 air (78% of the mass) contributes markedly by its mechanical effect on the rock or other mass, in conjunction with the high temperature and high velocity of the burner eflluent.

An example illustrates the favorable results possible using the principles of our invention. A conventional 600 s.c.f.m. air-fuel burner drills a 10-inch diameter hole in a particular taconite at 25 ft./hr. This burner operates with a chamber pressure of 70 p.si.g. with a jet nozzle diameter of 1.250 inches. Decreasing the nozzle diameter to .875 inch increases the chamber pressure to nearly 200 p.si.g. Of course, an air compressor of increased pressure output is required. The higher pressure unit, consuming the same 600 s.c.f.m. of compressed-air, drills an 8-inch hole at 35 ft./hr.; it is notable that while the volume of material removed in the latter case is actually less, the action is far more effective in producing the desired result in terms linear of drilling speed.

The principles of the invention may be better understood by inspecting the figures, where:

FIGURE 1 is a cross-sectional isometric view of a flame drilling operation.

FIGURE 2 is a longitudinal cross-sectional view of a burner capable of practicing the invention.

FIGURE 3 is a modification of the burner of FIGURE 1, by which abrasive particles may be introduced into the burner.

FIGURES 4a, 4b, and 4c are schematic views of rock surfaces impacted by flame jets of different velocity.

FIGURE 1 illustrates flame jet drilling of a heat-spallable material 13, for example, taconite. The internal burner 11 produces flame jet 15 which impacts against the advancing face 21 of the hole 12. Spalled material and the exhausting products of combustion 16 issue upward and out of the hole at ground surface 14. Flame jet 15 is supersonic and is characterized by shock diamonds 49 which are described in more detail in connection with the discussion of FIGURE 2. Burner 11 is held by tube 17 which serves also to conduct compressed-air from hose 19 to the burner. Oil, or other fuel, is introduced from hose 20 through tube 18 contained within the larger tube 17. An O-ring seal is provided between tube 18 and hose 20. As the hole is drilled, the burner apparatus is advanced at a corresponding rate.

A detailed view of an air fuel burner is shown in FIG- URE 2. This design may be referred to as a three-tube design which provides a compact, symmetric unit. Air for combustion passes from tube 17 into distribution chamber 39 and then to the forward, or nozzle, end of the burner through annular space 41 contained between outer tube 31 and the middle tube 32. The air then reverses direction as shown by the arrows to pass upward between tube 32 and an inner liner 33 into well cavity 44 through radially disposed holes 43 in end piece 38-. Oil passes into spray nozzle 37 from tube 18 to form spray cone 46 which mixes and burns with the compressed air in combustion chamber 45. The products of combustion expand from the elevated pressure region of chamber 45 through nozzle 47 to form flame jet 48. i

The burner itself is rather simple. In addition to the three tubes 31, 32, 33, there is a combustor end piece 38 and a nozzle piece 47 forms the forward face of the combustion chamber 45, being an integral part of that chamber by virtue of weld 52. In turn, the piece 38 forms the opposite face of the combustion chamber 45 and is integrally connected to liner 33 and with nozzle 47 by weld 53.

The middle tube 32 conducts the air flow to the forward end of the burner, this air flow providing adequate cooling of the outer tube 31 which is subject to heating by the exhausting hot gases passing up through the hole 12 (F IG- 3 URE l). Liner 33 operates red hot to facilitate the intense reactions taking place in chamber 45.

The elevated operating temperature of liner 33 causes a significant axial elongation of that tube. An 18-inch liner will expand thermally by as much as %-inch. To prevent warpage of the various tubes due to unequal expansion (the other two tubes 31 and 32 do not reach as high a temperature) free motion of the liner 33 relative to the tubes 31 and 32 must be provided. In previous designs, terminal element 38 and nozzle 47 were rigidly attached to outer tube 31 and liner 33 was allowed to move freely over the cylindrical portions of those outer pieces supporting tube 31. We have found that such a sliding arrangement presents a serious disadvantage due to unavoidable leakage of air caused by uneven expansion of these various parts. squealing of a very objectionable nature may result due to this leakage. Also, all the air is not used for regenerative cooling or for combustion. The tubes become hotter and less intense combustion results.

We provide a geometry which not only provides for free relative movement of the various burner tubes, but eliminates the possibility of air leakage. As seen in FIGURE 2, the lower end of the middle tube 32 is free to float and said tube can expand or contract independently of the amount of expansion of any of the other elements. The liner 33 may expand, and its elongation is accommodated by motion of tube 18, sliding on oil hose 20.

Further, the construction of the burner permits not only elongation of parts, but lateral displacement occasioned by any unequal heating around the circumference of the tubular elements. The oil hose 20 is not mechanically fixed, thus permitting such movement.

Although nozzle duct 47 is shown (in solid lines) as a converging nozzle, an expanding section 57 (in dotted lines) contained in nozzle piece 58 may also be used. The various portions of the flame jet issuing from nozzle 47 are due to the supersonic jet velocity of the flame itself. Shock diamonds 49 are characteristic of the situation where unbalanced gas pressures exist. At the exit plane of nozzle 47 the gas pressure (for high combustion chamber pressure) is much greater than that of the surrounding atmosphere. The jet expands as it passes into the atmosphere. But, due to the lower sound velocity as compared to the jet velocity, the jet pressure and atmospheric pressure do not immediately balance. Shock patterns result and the jet surface itself alternately expands and contracts.

The mechanism by which the higher velocity flame jets are capable of drilling faster and producing a smaller diameter hole is though to be that now described in connection with FIGURE 4. In the three views of FIGURE 4 assume that the same air and fuel flows exist. Further, the jet velocity of (b) is double that of (a) and that of double that of (b). With increased jet velocity, jet diameter is reduced. Also, we have found that the diameter of the burner itself may be made smaller at increased combustion pressures.

In FIGURE 4a assume V =1,500 ft./sec. This flame jet is subsonic and is characterized by drilling a relatively large diameter hole. The impacting gases must turn and pass radially away from stagnation point 74, since their momentum is relatively low. Thus, heat transfer to the rock is strongly governed by the component of the spreading gas velocity more or less horizontally along the rock surface. For a broad, low-velocity jet impaction, the tangential contact velocity gradient is relatively low. To illustrate, the increase of velocity from point 75 to point 76 (in unit distance) is not great. Low heat transfer near the stagnation point 74 results in a lower removal rate of the rock at the jet centerline. The hot gases expand outward and continue to spall the rock a relatively long distance away from the point 74. A large hole diameter results, with slow axial progress.

In FIGURE 4b assume V =3,O00 ft./sec., a value which would be associated with a chamber pressure of around 50 p.s.i.g. The impaction of the jet gases covers a smaller central area and the tangential speedup from stagnation point 84 to arrows 85 and 86 is much greater than for the previous case. A rather uniform rock removal rate results with the forward face of the hole being nearly hemispherical. The hole is smaller in diameter and the drilling rate is increased. However, the total amount of rock removed is less than for the case of FIGURE 4a.

The highest drilling rates (for the examples of FIGURE 4) with smallest drilled hole diameter results when the jet velocity V is increased to 6,000 ft./sec. For an air-fuel mixture, the corresponding chamber pressure would be about 300 p.s.i.g. Here, the tangential velocity increase radially outward from stagnation point 94 is immediately very high, leading to an actual cutting rate which is higher at the hole center than further out. Although the least amount of rock volume may be removed, the speed of hole advance is greatest. Hole diameter is held to a dimension only slightly larger than overall burner diameter.

By increasing the chamber pressure significantly higher than currently practical in flame jet drilling, greatly increased drilling rates result, where air provides the necessary oxidant and the inert component of air contributes to the mass flow at high temperatures and velocities.

A practical set of values for a burner to successfully practice the method of our invention is given in the following table:

Air supply 600 s.c.f.m. at 250 p.s.i.g. Nozzle bore 0.875 inch.

Fuel #2 oil, 26 gallons per hr. Liner 18' long; 2'' ID.

Outer tube, O.D. 3".

Outer tube wall A" thick.

Middle tube wall A" thick.

Chamber pressure 190 p.s.i.g.

Jet temperature 3000 F.

Jet velocity A 5200 ft./sec. (10 shock diamonds).

Where abrasive drilling is used either alone or in conjunction with flame drilling, the increased jet velocity of our invention adds significantly to the erosion action of the particles as they impinge on the rock with increased kinetic energy. Again, increased drilling rates result while hole diameters are reduced. FIGURE 3 illustrates a burner geometry providing for free motion of the unitized combustor, yet allowing abrasive particles to be fed into the combustor. Abrasive feed tube 65 is firmly held by end piece 38. The well cavity 44 is offset enough to permit the addition of the tube 65. The fuel is provided as before and abrasive particles are airborne through tube 65 and become part of the burner eflluent.

For the purposes of this invention, the term internal burner applies to a combustion device wherein the oxidant and fuel are fed at a relatively steady rate into a chamber where combustion proceeds continuously. Devices which rely on one or more explosion reactions are not considered to be internal burners by this definition.

While we have described a particular burner device for practicing our invention, its scope comprehends the novel general method of drilling, channelling and otherwise working minerals, rocks or soils.

We claim:

1. The method of flame jet drilling and channelling a solid body using an internal burner as the heat source and air as the oxidant comprising operating said burner at a combustion chamber pressure greater than p.s.i.g. and directing the resulting flame jet against said body.

2. The method according to claim 1 in which said body is a mass of rock.

3. The method according to claim 1 in which said body is soil.

4. The method according to claim 1 in which said body is a mineral material.

5. The method according to claim 1 including the step of adding abrasive particles to the jet stream effluent of said burner.

6. The method according to claim 5 in which said References Cited UNITED STATES PATENTS Burch 17513 Smith et a1 17513 X Browning 51-8 Browning 17514 Ross 17514 Margilofi 17513 X Browning 175-14 DAVID H. BROWN, Primary Examiner U.S. Cl. X.R.

Keefer 51-8 X 51 3z1; 175--13 Murphy, et a1. 17513 

